Conventional digital cameras have made use of a zoom lens system with which the object distance of an in-focus subject (hereinafter referred to as the subject distance) can be kept substantially constant while the focal length is changed. For example, a zoom lens system is employed in compact digital cameras and interchangeable lens-type digital cameras.
For example, with a conventional lens barrel, as the zoom mechanism is operated, a focus lens unit that includes a focus lens is moved by a cam mechanism in the optical axis direction. This allows the subject distance to be kept substantially constant while the focal length is changed (See Patent Citation 1, for example).